Stability Of Food Emulsions Research Articles

Antioxidant Activity of Plant Phenols: Chemical Mechanisms and Biological Significance

Polyphenols having catechol (1,2-dihydroxybenzene) nuclei are strong in vitro antioxidants owing to their ability to rapidly reduce reactive oxygen species (ROS), bind transition metal ions as inert complexes and regenerate the potent chain-breaking antioxidant ? -tocopherol. Polyphenols provide antioxidant protection to plants by acting as electron donors to peroxidases that reduce hydrogen peroxide into water. Polyphenols are also likely to improve the oxidative stability of food emulsions by binding metal ions and/or reducing ROS at phospholipid or protein interfaces. This protection may extend to the gastric compartment where millimolar concentrations of polyphenols can accumulate after consumption of a meal rich in plant products. Beyond the digestive tract, direct antioxidant effects become quite hypothetical as polyphenols are only poorly absorbed and mostly converted into weakly reducing metabolites. However, despite the low circulating concentrations of polyphenol metabolites, ROS-scavenging and/or inhibition of ROS-producing enzymes could still operate provided that polyphenol metabolites accumulate on the very sites of oxidative stress and inflammation. Finally, oxidation of polyphenols in cells can lead to electrophilic/oxidizing metabolites with a capacity to up-regulate genes coding for antioxidant enzymes. In conclusion, the ability of polyphenols to act as antioxidants in humans must be severely qualified. Keywords: Polyphenols, Flavonoids, Antioxidant, Reactive oxygen species, Oxidative stress, Radicals, Bioavailability, Mechanism, cardiovascular disease (CVD), age-related disorders, reactive oxygen species (ROS), ORAC (oxygen radical absorbance capacity), lipoxygenases (LOX), cycloxygenases (COX), leukotrienes

Mixed biopolymers at interfaces: Competitive adsorption and multilayer structures

Mixed biopolymer layers are commonly involved in the stabilization of food emulsions and foams. The interfacial composition and structure of mixed layers are predominantly determined by two mechanistic phenomena—competitive adsorption from mixed solution and cooperative adsorption into multilayers. The surface-active protein components typically dominate primary layers around droplets and bubbles, and the interacting polysaccharides form outer secondary stabilizing layers. This article reviews progress in understanding the factors controlling the nanoscale structure and physico-chemical properties of adsorbed layers in colloidal systems containing mixtures of biopolymers. Contributions from different experimental techniques are described, with particular attention directed towards the role of surface shear rheology in providing information on competitive adsorption of proteins and macromolecular interactions at fluid interfaces. We also consider here the phenomenon of phase separation in mixed protein monolayers, the balance of thermodynamic and kinetic factors in determining biopolymer layer properties, and the involvement of electrostatic interactions in the stabilization of emulsions by protein–polysaccharide complexes.

Interaction Between Polar Components and the Degree of Unsaturation of Fatty Acids on the Oxidative Stability of Emulsions

AbstractMinor components (polar components) and the degree of unsaturation of the fatty acids are the main factors responsible for the oxidative stability of bulk oils and emulsions. The isolated effects of these two factors and their interaction were evaluated in oil–in‐water emulsions stored at 32 °C. Samples of coconut, olive, soybean, linseed and fish oils, both full and stripped of their polar components, were used to prepare the emulsions (1% w/w). The maximum concentration of hydroperoxide (LOOHmax) and the rate of formation of hydroperoxides (μmol L−1 h−1) were used to measure the primary products. Hexanal, propanal and malondialdehyde were used to determine the secondary products of the oxidized emulsions containing polyunsaturated fatty acids. LOOHmax varied from 0.16 to 12.75 mmol/kg among the samples. The interaction between the polar components and the degree of unsaturation of the fatty acids was significant (p < 0.001) when the hydroperoxides were evaluated. In general, the degree of unsaturation (β1) and the absence of polar components (β2), respectively, represented 30 and 20% of the contribution to increase the mean oxidation, with the interaction (β12) contribution being more sensitive to the rate of formation of hydroperoxides (16%) than to the LOOHmax (5%). The significance of this interaction suggests that both strategies present synergism and should be applied to improve the oxidative stability of food emulsions.

Stability of protein‐stabilised β‐carotene nanodispersions against heating, salts and pH

AbstractBACKGROUND: Milk proteins are used in a wide range of formulated food emulsions. The stability of food emulsions depends on their ingredients and processing conditions. In this work, β‐carotene nanodispersions were prepared with selected milk‐protein products using solvent‐displacement method. The objective of this work was to evaluate the stability of these nanodispersions against heating, salts and pH.RESULTS: Sodium caseinate (SC)‐stabilised nanodispersions possessed the smallest mean particle size of 17 nm, while those prepared with whey‐protein products resulted in larger mean particle sizes (45–127 nm). Formation of large particles (mean particle size of 300 nm) started after 1 h of heating at 60 °C in nanodispersions prepared with SC. More drastic particle size changes were observed in nanodispersions prepared with whey protein concentrate and whey protein isolate. The SC‐stabilised nanodispersions were fairly stable against Na+ ions at concentrations below 100 mmol L−1, but drastic aggregation occurred in ≥ 50 mmol L−1 CaCl2 solutions. Aggregation was also observed in whey protein‐stabilised nanodispersions after the addition of NaCl and CaCl2 solutions. All sample exhibited the smallest mean particle size at neutral pH, but large aggregates were formed at both ends of extreme pH and at pH around the isoelectric point of the proteins.CONCLUSION: The nanodispersions prepared with SC were generally more stable against thermal processing, ionic strength and pH, compared to those prepared with whey proteins. The stable β‐carotene nanodispersions showed a good potential for industrial applications. Copyright © 2008 Society of Chemical Industry

Interfacial structure and stability of food emulsions as affected by protein-polysaccharide interactions.

The exploitation of protein-polysaccharide interactions offers opportunities for the design of new ingredients and interfacial structures with applications in the food and pharmaceutical industries. Association of protein and polysaccharide molecules may occur chemically through covalent bonds or physically through electrostatic interactions. Theoretical and experimental studies indicate that various molecular and thermodynamic factors can be adjusted to optimize the effectiveness of covalent conjugates and electrostatic complexes in the stabilization of interfaces, gels and emulsions. Maillard-type protein-polysaccharide conjugates have excellent emulsifying and steric stabilizing properties, especially under conditions where the protein alone is poorly soluble. Charged polysaccharides form soluble complexes or coacervates with proteins depending on pH, ionic strength, and biopolymer charge distribution. The structure and stabilizing properties of the mixed protein + polysaccharide layer depends on the sequence of adsorption of the biopolymers to the interface. There is good potential for use of interfacial protein-polysaccharide complexes in the nanoscale engineering of delivery vehicles for nutrient encapsulation and in the protection of adsorbed proteins and emulsified lipids against enzymatic breakdown during digestion.

Critical Review of Techniques and Methodologies for Characterization of Emulsion Stability

The efficient development and production of high quality emulsion-based products depends on knowledge of their physicochemical properties and stability. A wide variety of different analytical techniques and methodologies have been developed to characterize the properties of food emulsions. The purpose of this review article is to provide a critical overview of the most important properties of emulsions that are of interest to the food industry, the type of analytical techniques that are available to measure these properties, and the experimental protocols that have been developed to characterize the stability of food emulsions. Recommendations are made about the most suitable analytical techniques and experimental protocols needed to characterize the stability and properties of food emulsions.

Effect of Depletion Force on the Stability of Food Emulsions

The stability of food emulsions containing milk proteins and sucrose ester was studied by measuring the creaming velocity of an oil‐in‐water emulsion. The inter‐droplet interaction was quantified by measuring the radial distribution function using an advanced digital imaging technique. The phenomenon of protein sub‐micelles layering inside the film formed between the adjacent droplets was observed by using the capillary force balance apparatus. The attractive interaction of the droplets was attributed to the depletion force induced by the protein sub‐micelles in the film. The experimental results on creaming velocity were rationalized in terms of a statistical thermodynamic model, which takes into account the attractive inter‐droplet interactions.

Effect of Protein on the Texture of Food Emulsions under Steady Flow

The texture of food emulsions was quantified as the structure factor using the backlight scattering technique. The change of the texture of food emulsions under steady flow was monitored in terms of the structure factor. The role of different types of protein (sodium caseinate and soy protein) on the change of texture of food emulsions under steady flow was studied. The emulsion stabilized by sodium caseinate was more stable under steady flow than the food emulsion stabilized by FP940 (partially hydrolyzed soy protein). The layering of caseinate submicelles in the film between the fat particles was suggested as a reason for the greater stability of the sodium caseinate stabilized emulsion under steady flow. The FP940 stabilized emulsion showed a sudden change of texture at a shear rate of 200 rad/s (the threshold), while the sodium caseinate stabilized emulsion was relatively stable under this shear rate. The FP940 stabilized food emulsion with a high fat concentration had a more ordered texture, represented as a greater structure factor; however, this texture degraded quickly under steady flow. Versa Whip 500 (highly hydrolyzed soy protein) was compared with FP940 (partially hydrolyzed soy protein) for their effects on the stability of food emulsions under steady flow. The stability of a food emulsion under steady flow improved as the concentration of Versa Whip 500 (highly hydrolyzed soy protein) increased from 1 to 2.5 wt % in the aqueous phase. The Versa Whip 500 stabilized emulsion had soy protein micelle layering in the film between the fat particles, which helped to stabilize the fat particles under steady flow.

Shear-induced fat particle structure variation and the stability of food emulsions: II. Effects of surfactants, protein, and fat substitutes

The shear-induced fat particle structure variation and stability of food emulsions were investigated by the back-light scattering technique. The effects of surfactants (including water-soluble and oil-soluble surfactants), protein, and fat substitutes on the fat particle packing structure and stability of food emulsions were studied. It was found that protein plays a very important role on the food emulsion stability under shear stress by the formation of an adsorption layer on the surface of fat particles and microlayering of protein submicelles around fat particles. The addition of a fat substitute into low-fat food emulsions decreases the fat particle packing structure due to the irregular shape and large size of the fat substitute particles.

Shear-induced fat particle structure variation and the stability of food emulsions: I. Effects of shear history, shear rate and temperature

The shear-induced fat particle structure variation and the stability of food emulsions were investigated by the back-light scattering technique. The effects of temperature, shear rate, and shear history on the fat particle structure and stability of food emulsions were studied. Increasing the shear time initially improves the fat particle structure; afterwards, the fat particle packing structure becomes less ordered. The effect of temperature on the fat particle structure is complicated. It was also found that the optimal temperature, shear rate and shear history exist in order to obtain a well-developed fat particle structure. A qualitative explanation of the experimental results is provided.

Analysis of stability of food emulsions by Eyring's Theory: Influence of different biopolymers

Eyring's kinetic theory of liquids was applied to the study of flow behavior of low oil content mayonnaises at different temperatures. These food emulsions were formulated with different biopolymers as stabilizers (polysaccharides such as modified starch, gellan gum, and pectin). The analysis of the values obtained for the parameters of the Eyring equation for viscosity determined the emulsion containing only starch as a stabilizer is the most unstable to stirring. Replacement of part of the starch with gellan gum or pectin enhances the stability of the emulsion. The results for activation energy are quite similar for high shear rates, which can be explained by the evolution of the average drop size distribution. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2653–2657, 2004

Analysis of stability of food emulsions by Eyring's theory: Influence of different biopolymers

AbstractEyring's kinetic theory of liquids was applied to the study of flow behavior of low oil content mayonnaises at different temperatures. These food emulsions were formulated with different biopolymers as stabilizers (polysaccharides such as modified starch, gellan gum, and pectin). The analysis of the values obtained for the parameters of the Eyring equation for viscosity determined the emulsion containing only starch as a stabilizer is the most unstable to stirring. Replacement of part of the starch with gellan gum or pectin enhances the stability of the emulsion. The results for activation energy are quite similar for high shear rates, which can be explained by the evolution of the average drop size distribution. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2653–2657, 2004

Singlet Oxygen Quenching Effect of Quercetin in Erythrosine-Sensitized Photooxidation of Oil-in-Water Emulsion

Oxidation reaction can be initiated by either diradical triplet oxygen or non radical singlet oxygen. The singlet oxygen can be formed infoods from triplet oxygen by photosensitized reaction. This research was intended to study the quenching effect of quercetin on lipid oxidation rate in the erythrosine-sensitized photooxidation of oil-in-water emulsion. Palm oil-in-water emulsion, containing erythrosine 100 ppm and quercetin 0, 25, 50, 75 and 100 ppm, were prepared with polyoxyelhylene 100 stearyl ether (Brij 700) or polyoxyethylene sorbitan monolaurate (Tween 20). Structurally Brij 700 has 5 times longer polyoxyethylene groups than Tween 20. The mixture were stored under 4000 luxfluorescent light for 10 h and peroxide values were measured at 2 h interval. Erythrosine effectively sensitized the photooxidation of palm oil-in-water emulsion, as expected. Lipid oxidation rates, as determined by the formation of lipid hydroperoxides and headspace oxygen, in palm oil-in-water emulsions containing erythrosine decreased with increasing quercetin concentration. At pH 3, the peroxide value was higher than at pH 7. Brij 700 decreased production of lipid hydroperoxides from palm oil-in-water-emulsions compared to emulsions stabilized by Tween 20. The results indicate that quercetin is an efective singlet oxygen quencher in palm oil-in-water emulsion and the surfactant headgroup size could be an important determinant in the oxidative stability of food emulsions.

Protein-Polysaccharide Interactions for Stabilization of Food Emulsions

Protein-Polysaccharide Interactions for Stabilization of Food Emulsions

Protein-Polysaccharide Interactions for Stabilization of Food Emulsions

ABSTRACT Proteins, polysaccharides and their blends, as examples of natural biopolymers, are surface active materials. Biopolymers may be considered as amphiphilic macromolecules that play an essential role in stabilizing food formulations (foams, emulsions and dispersions). Under specific conditions (such as protein-to-polysaccharide ratio, pH, ionic strength, temperature, mixing processing), it has been stated that proteins and polysaccharides form hybrids (complexes) with enhanced functional properties in comparison to the proteins and polysaccharides alone. Different protein-polysaccharide pairs are reviewed with particular attention to the emulsification capability of their mixtures. In the case of uncomplexed blends of biopolymers, competitive adsorption onto hydrophobic surfaces is generally reported. Conversely, electrostatic complexation between oppositely charged proteins and polysaccharides allows better anchoring of the new-formed macro-molecular amphiphile onto oil-water interfaces. Moreover, improved thermal stability and increased resistance to external treatment (high pressure) involved in food processing are obtained. This review presents basic and applied knowledge on protein-polysaccharide interactions in aqueous medium and at the oil-water interface in food emulsion systems. Electrostatic interactions and thermodynamic incompatibility in mixed biopolymer solutions are correlated to the functional properties (rheology, surface hydrophobiciry, emulsification power) of these interesting blends. Basic and industrial selected systems of different families of hydrocolloids (as gum Arabic, galactomannans, pectins) and protein (caseins, whey, soya, gelatin) mixtures are reviewed.

Ability of surfactant headgroup size to alter lipid and antioxidant oxidation in oil-in-water emulsions.

Oxidation of oil-in-water emulsion droplets is influenced by the properties of the interfacial membrane surrounding the lipid core. To evaluate how surfactant headgroup size influences lipid oxidation rates, emulsions were prepared with polyoxyethylene 10 stearyl ether (Brij 76) or polyoxyethylene 100 stearyl ether (Brij 700), which are structurally identical except for their hydrophilic headgroups, with Brij 700 containing 10 times more polyoxyethylene groups than Brij 76. Fe(2+)-promoted decomposition of cumene hydroperoxide was lower in Brij 700-stabilized than in Brij 76-stabilized hexadecane emulsions. Fe(2+)-promoted alpha-tocopherol oxidation rates were similar in hexadecane emulsion regardless of surfactant type. Brij 700 decreased production of hexanal from methyl linoleate and the formation of lipid peroxides and propanal from salmon oil compared to emulsions stabilized by Brij 76. These results indicate that emulsion droplet interfacial thickness could be an important determinant in the oxidative stability of food emulsions.

Ability of iron to promote surfactant peroxide decomposition and oxidize alpha-tocopherol.

Peroxides are an important factor in oxidative reactions in foods because their decomposition can result in formation of highly reactive free radicals. Emulsifiers such as the Brijs, Tweens, and lecithin were found to contain 4-35 micromol of peroxides/g of surfactant. Peroxide concentrations in Tween 20 micelles increased in the presence of low iron concentrations but decreased when iron concentrations were high, suggesting that iron was capable of promoting both peroxide formation and decomposition. Oxidation of alpha-tocopherol was observed in micelles high in peroxides (Tween 20) but not in micelles where peroxide concentrations were low (Brij). Transition metals accelerated the oxidation of alpha-tocopherol in Tween 20 micelles, whereas EDTA stabilized alpha-tocopherol in the presence of added Fe(2+). These results suggest that surfactant peroxides could decrease the oxidative stability of food emulsions by acting as a source of free radicals, especially in the presence of transition metals.

Fat Particle Structure and Stability of Food Emulsions

ABSTRACTWe used a nondestructive Kossel diffraction technique based on the principle of backlight scattering to characterize the structure formation in concentrated model food emulsions. We also measured the effects of temperature, shear, casein micelles and gum on the fat particle packing structure in such systems. Through this technique, we demonstrated the effects of casein micelles on the pair potential of fat particle interactions and shelf life of such systems. We carried out theoretical calculations using a statistical mechanics approach by numerically solving the Ornstein‐Zernike equation with Percus‐Yevick closure for a bidisperse system consisting of fat particles and micelles, and showed that the experimental results were consistent with theoretical simulations.

Wetting of fat crystals by triglyceride oil and water. 2. adhesion to the oil/water interface

AbstractFat crystals influence the stability of food emulsions, such as margarine, butter, or cream, if adsorbed to the oil/water interface. During the adsorption process, a new fat crystal/water interface is created, while the oil/water interface is lost. The driving force for adsorption is therefore the difference between the interactions between fat crystal/water and oil/water. In this work, we have estimated this interaction difference and compared it to the displacement energy for fat crystals from the oil/water interface to the oil. Our calculations have shown that fat crystal adsorption to the oil/water interface (expressed by contact angle ϑ) is determined by polar energy, excess of fat crystal/water over oil/water (Isw ‐Iow). The interfacial tension constitutes the resistance force for crystal adsorption to the interface. Polar interaction energy for fat crystal/water is stronger than the polar interaction energy for oil/water in all cases examined (Isw ‐Iow >0). The difference corresponds to about 104–106 hydrogen bonds for a hypothetical fat crystal with a diameter of 1 µm. The displacement energy for fat crystals to oil is lower than the polar energy excess in most cases examined. Thus, an additional interaction between fat crystals and oil makes it easy to displace the crystals to the oil. There is also a relationship between the adhesion tension (‐γow • cos ϑ) for the crystals at the oil/water interface and the interfacial tension γow. A straight line of slope ‐1 is achieved for systems with low interfacial tensions (γow) and low polar energy excess (Isw ‐Iow).

Investigation of the mechanisms of stabilization of food emulsions by vegetable proteins

A number of experimental methods have been used for investigation of the microhetero-geneous components of corn oil in water emulsion systems stabilized with tomato seed protein isolate. Light-scattering studies on the initial aqueous protein solution have shown the presence of protein aggregates much bigger than single molecules. The dilational behavior of oil/water interfaces after a swift expansion or compression was found to comply with the rheological model of Maxwell (see reference 27). Observations of the thin aqueous films between oil phases allow us to suggest that the presence of protein aggregates inside the film, the electrostatic repulsion and the surface viscoelasticity are factors contributing to the film stability. A comparison with other vegetable protein speices (from soya and lupine beans) is performed in some of the experiments. The measurements of the stability of batch emulsions show that the studied protein isolates act as effective stabilizing agents.